Legalizing an Illegal Addition in Sacramento

[Robert Jensen]

How can one make an illegal unit, legal? Has anyone gone through the process? 

Looking to buy a house in Sacramento that has 600 sq feet of illegal added additions. They look professionally done -- match the existing house perfectly. The house is priced without considering this extra space. 

I come across this sort of thing often and have always wanted to know the process of legalizing these un permitted structures. Is it really that difficult?